Commercialization of an extra high-voltage nonflammable transformer

A perfluorocarbon (PFC)-immersed 275-kV transformer with compressed SF₆, gas has been developed. This paper describes the basic cooling and insulation characteristics of PFC, the ac partial discharge voltage, and the aging of PFC-immersed insulation. The results demonstrate that a prototype 275-kV 100-MVA three-phase transformer can be operated without any difficulties for an extended period of overvoltage. This prototype has an ac partial discharge initiation strength which is 1.5 times that of the ac test voltage and a lightning impulse breakdown strength which is 1.5 times that of the test voltage. A 275-kV 250-MVA three-phase transformer was built and is being operated at the Abe substation of Chubu Electric Power Co., Inc. The transformer has been operating satisfactorily.     

电网严重故障下的电压稳定应对措施分析

台风、雷电和冰灾等自然灾害现象难预测、不受控。这些灾变天气不仅严重影响人们的生产生活,而且也给电网运行带来危害,因此越来越受重视。2019年8月9日英国发生的雷击引发停电事件,再次给国内外电网运行安全敲响了警钟。首先分析了英国8.9大停电事件发展过程,揭示雷击引起的系统电压下降、频率下跌的连锁反应情况。接着研究了含风电的电力系统电压稳定性及无功补偿容量计算方法,并以某典型地区电网为例,对严重故障下的电网稳定性进行仿真分析。提出防止系统电压失稳的应对措施,最后给出提高电网运行安全稳定性的相关措施建议。     

Study of a future metropolitan electric network adapted to introduction of cryogenic high-power cables

The authors have investigated the operational feasibility of a future metropolitan electric power system associated with highly densified cryogenic cables. A new concept of power system configuration with cryogenic cables and its operation have been proposed. Three different models of future power transmission systems in large cities of Japan have been constructed as the background systems prior to introduction of cryogenic cables in the 21st century. This paper considers one of the three models which is characterized by its conventional transmission system constructed mainly by 154-kV transmission lines stepping down directly from the 500-kV outer ring without any intermediate voltage class. This paper also discusses whether or not the power system model will be operated effectively together with cryogenic cables to supply demands forecasted in the period subsequent to the first decade of the 21st century. The computer simulations are carried out to obtain power flow and bus voltage distributions for a peak load period as well as for an off-peak one in the power system model. These simulations reveal that the conventional background power system should be arranged very carefully before introducing the cryogenic cables to facilitate their operations. (1) On a contingent trip of a cryogenic cable in the peak in the peak load period, not all bus voltages are expected to be kept within a tolerant zone due to the high impedance of 154-kV conventional transmission lines in the power system model. (2) Thus it is proposed that the background conventional system prior to introduction of cryogenic cables should be developed not only by extension of 154-kV conventional transmission lines but also by introduction of 275-kV lines. (3) Bus voltage rises induced in the off-peak load period are reduced by effective utilization of 275-kV conventional transmission lines.     

A dynamic load model for analysis of power system voltage

It has become important in recent years that power systems be protected from voltage instability caused, in part, by heavy loads and the concentration of air conditioning loads during certain hours. Many studies have explored the problems and possible countermeasures. However, the load representations used in these studies are based on power values, i.e., P and Q; therefore, these analytic models are insufficient to express load responses and, thus, investigation is somewhat limited. This paper introduces a load model expressing load admittance responses by a first-order delay differential equation and uses this model in tandem with power network solutions to analyze power system voltage stability. This load model is shown to work reliably and effectively. Using this model, it is possible to investigate more precisely and widely than before the power system voltage stability phenomenon of arbitrary characteristic loads in lower voltage ranges and on propagations of instability through the networks.     

Development of a new detection method of partial discharge for EHV long-distance active cable line

A new method was used to measure the characteristics of partial discharge (PD) for an active 9.5-km long-distance 275-kV XLPE cable line with insulating joints. It was found that the detection of PD and the calibration of detection sensitivity were carried out safely and easily. The proposed method includes:

• 1 detection of PDs and injection of calibration pulses using two pairs of metal electrodes placed on PVC jackets with anti-corrosion layers separated by a joint sleeve sectionalizing insulator;
• 2 measurement of detection sensitivity with distance using calibration pulses injected from an adjacent insulating joint;
• 3 detection of PDs with a high S/N ratio measured at a frequency corresponding to the lowest noise level; and
• 4 usage of rf cores attached at cross-bonding leads and wires for sheath current limiters to reduce the crosstalk of signal and noise through these lines at insulating joints.

Using a combination of these techniques, the highest detection sensitivity was 1 pC in the vicinity of an insulating joint, and 15 pC at 617 m from the adjacent joint. The sensitivity obtained by the conventional PD measurement using a low-frequency method was at most 1000 pC.     

柔性直流系统挤出绝缘电缆暂态过电压仿真

电压源换流器高压直流(VSC HVDC)输电系统中广泛应用了挤出绝缘直流电缆。针对开关操作、内部故障以及雷击所引起的暂态过电压对直流电缆系统可靠性的挑战,基于南澳柔性直流输电示范工程,利用PSCAD/EMTDC建立直流电缆系统仿真模型,设置交流单相接地、两相短路、桥臂电抗器接地等不同类型的故障,分析了各类故障条件下直流电缆系统的暂态过电压特性。研究结果表明,直流电缆端部过电压峰值最大可达2 p.u.,且电缆端部出现的过电压幅值与短路电阻值有关。     

Ultralow power voltage reference circuit for implantable devices in standard CMOS technology

An ultralow power CMOS voltage reference for body implantable devices is presented in this paper. The circuit core consists of only regular threshold voltage PMOS transistors, thus leading to a very reduced output voltage dispersion, defined as σ/μ, and extremely low power consumption. A mathematical model of the generated reference voltage was obtained by solving circuit equations, and its numerical solution has been validated by extensive electrical simulations using a commercial circuit simulator. The proposed solution incorporates a passive RC low-pass filter, to enhance power supply rejection (PSR) over a wide frequency range, and a speed-up section, to accelerate the switching-on of the circuit. The prototype was implemented in 0.18 μm standard CMOS technology and is able to operate with supply voltages ranging from 0.7 to 1.8 V providing a measured output voltage value of 584.2 mV at the target temperature of 36° C. The measured σ/μ dispersion of the reference voltage generated is 0.65% without the need of trimming. At the minimum supply of 0.7 V, the experimental power consumption is 64.5 pW, while the measured PSR is kept below –60 dB from DC up to the MHz frequency range.     

Characteristics and classification of high-current fault arcs on distribution systems

When a fault occurs on transmission or distribution systems due to lightning or overvoltage, often an arc discharge occurs at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission, etc., thus it sometimes causes heavy damages to electric power equipment. The arc discharge is influenced by the conditions around the arcs, i.e., gas, insulation materials, gap length, weather, etc. Also, the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occurred. In this paper, the arc voltage data in 6-kV class XLPE cables and 6-kV class overhead lines are analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selected.     

一种动态电压恢复器研究

针对现代机场直线加电系统中存在的电缆压降问题,提出了一种解决方案,即通过在变换器后加装动态电压恢复器来补偿电缆的压降.动态电压恢复器采用单向馈能电路结构,可以在能量单向流动的情况下,实现对因电缆压降而产生的电压暂降或暂升的持续补偿.基于该动态电压恢复器结构,分析了负载电压有效值反馈控制方法.理论分析和试验结果表明,动态电压恢复器可有效补偿电缆压降,并能保证负载电压的稳定.     

Line Arresters Application in Lightning Protection of High Voltage Substations with Non-standard Configuration

In this paper, application of gapless transmission line arresters (TLAs) in substation lightning protection is analyzed. Deterministic calculations in accordance with IEC 62305 are performed. Substations with non-standard configuration equipped with Gas Insulated Switchgear (GIS), long cables, and a direct cable connecting GIS and power transformer are considered. It is concluded that 220- and 400-kV substations lightning performance can be significantly improved by using TLAs at only one or two overhead line towers in front of the substation. In some cases, TLAs provide better lightning protection of power transformer than surge arresters installed in GIS. Positive effects of TLAs application are noticed both in the case of back-flashovers and in the case of shielding failures. TLAs energy stress increases with the decrease of the system rated voltage. Maximum estimated values in the analyzed substations are below 2.5 and 0.5 kJ/kVr for TLAs installed in 220- and 400-kV systems, respectively.     

Development of a positive creeping discharge along an aerial insulated wire

In high‐voltage aerial distribution systems, the insulated cables are supported by the binding wire with the post insulator at the utility pole. When a lightning strike occurs in the neighborhood of the insulated cable in an aerial power distribution system, inductive lightning surges invade the central line of the cable. Then, creeping discharges develop along the cable surface from the binding wire tip at the same time as flashover of the post insulator at a supporting point of the cable. If the cable insulator has weak points such as pinholes, a malfunction near the cable supporting point may occur, with melting of the wire due to punch‐through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated cable caused by the lightning strike. The polarity of creeping discharges depends on the polarity of the inductive lightning surges, and the extension length and aspect of the discharge differ greatly depending on the discharge polarity. The development of these creeping discharges is attributed to complicated behavior of the positive and negative electric charges. In the present study, we examined in detail the development of a positive creeping discharge along a wire surface by using a high‐speed image converter camera. This paper describes the mechanism of development of a positive creeping discharge based on the experimental results. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 20–29, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20997     

核电站核岛直流系统电压报警定值分析与设计

利用RCC-E关于直流系统电压性能异常变化范围的规定,以及现有核岛直流系统蓄电池年度放电曲线,结合法国EDF核电站核岛直流系统电压高低报警定值,提出了1000 MW核电机组核岛直流系统电压高、低报警定值设计的新方法.电压报警定值按照系统设计方法,电压高报警定值与下游电源匹配,电压低报警后,蓄电池应能再运行半个多小时.运...     

A pulsed power supply with sag compensation using controlled gradational voltage

A pulsed power supply with sag compensation using controlled gradational voltage to increase the flatness of output waveforms has been developed. The sag compensation circuit consists of compensation units connected in series. Each compensation unit consists of capacitances, diodes, and semiconductor switches. The capacitances of each unit are charged with different voltages by 2ⁿ(V₀,2V₀,4V₀,…). The compensation voltage, which has 2ⁿ?1 steps, is generated by switching the semiconductor switches of each unit in a binary sequence. Using this method, compensation voltage waveforms up to 6.2 kV with 31 steps can be obtained with five compensation units. The sag compensation circuit has been adapted to a direct switch‐type pulsed power supply, which generates 7 kV pulsed voltage with a pulse width of 700µs, thus realizing sag compensation. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 54–63, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20017     

Influence of AC-DC parallel interconnection on voltage stability of AC systems

The static and dynamic characteristics of power supply to each node in a hybrid ac-dc power system are analyzed by means of static and transient P-V curves. Three kinds of dc transmission control scheme are compared. DC transmission systems are more effective in delivering power to inverter nodes. The constant firing angle, constant current control techinque provides more power to inverter nodes than the conventional constant current, constant voltage and constant power, constant extinction angle techniques. Transient digital simulations indicate that dc interconnection improves voltage stability to both the opening of a dc interconnected line and one-line opening of ac double-circuit interconnected lines.     

Study concerning production of lightning overvoltages on low‐voltage power distribution lines

In order to study lightning problems of low‐voltage power distribution lines, lightning overvoltage waveforms were observed inside the homes of customers. The cause of lightning overvoltages was examined from observation of striking points by still cameras. Lightning overvoltages of 62 waveforms were recorded by observation over a period of about 3 1/2 years. Observed waveforms can be classified into three types of single polarity (positive or negative), both polarities (which change from positive to negative or negative to positive), and pulsive waveform. The causes of these lightning overvoltages which were estimated from striking points are shown as follows: (1) Induced lightning overvoltages on low‐voltage distribution lines. (2)   Electric potential rise due to discharge of surge arresters or current of overhead ground wire. (3)   Shift of lightning overvoltages from high‐voltage side of transformer to low‐voltage side, which is due to electromagnetic induction. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 66–75, 2000     

Transient voltage stress of 400 kV urban system evaluated by numerical calculations

Overhead lines, high voltage cable systems and substations are important elements of the high voltage network. More and more close combinations of these elements are used in urban networks. This leads to new transient situations and a more complex transient behaviour in case of lightning or switching events. Additionally the requirements of a constant power supply ask for new efforts to predict impacts caused by interruptions.     

Use of multifield induction machine to determine the characteristics of self-excited generator systems at variable speed,constant voltage and constant frequency

This paper considers a generator system using variable energy such as wind power. The variable energy influences the voltage and frequency of a generator system. However, the load requires constant voltage and frequency. Therefore, this paper proposed that a generator system have the following good points:

• (1) This generator is a brushless system which makes use of the multifield induction machine;
• (2) Frequency converter of small capacity which is used for constant voltage and frequency in load at variable speed;
• (3) The PWM inverter can supply reactive power to the self-excited generator; and
• (4) Voltage wave of load is sine wave by LC filter of the frequency converter.

The multifield induction machines of this generator system have 4 poles and 8 poles similar to stator winding. The rotor of the multifield machine is especially cage type. This rotor can transform among the 4-pole field and 8-pole field on the stator. In this paper, an experimental study of the brushless, self-excited, constant voltage, constant frequency, variable speed and sine wave generator system by multifield induction machine is described. The component of this generator system, operation of multifield induction machine, characteristics of generator system, and the effect of LC filter in frequency converter are described.     

直流电缆雷电冲击电压安全裕度研究

高压直流电缆是柔性直流输电技术的关键装备,直流电缆的绝缘厚度设计以雷电冲击电压安全裕度为重要依据。为了获得直流电缆的安全裕度,文中提出了直流电缆雷电冲击电压安全裕度试验方法,建立了相应的试验回路,对冲击电压波形参数进行了计算、仿真和验证,获得了波前时间为1~5μs、半峰值时间为40~60μs的冲击电压波形;提出了直流电缆雷电冲击电压安全裕度的分析方法,计算了电缆绝缘的电场分布。研究表明,文中所提方法可以获得直流电缆的雷电冲击电压安全裕度,为高压直流电缆绝缘厚度设计提供了依据。     

Characteristics of discharge induced by laser-generated plasmas in atmospheric air

The possibility of laser-induced lightning has been investigated for the future application in the protection of electric power systems from lightning strokes. This technique induces lightning strokes artificially along a laser-produced breakdown plasma channel and conducts them to a harmless place on the ground. To clarify the plasma formation mechanism and the discharge (sparkover) induction process, sparkover induction experiments are performed for two types of long-gap electrode configurations, plate-to-rod and plate-to-plate, with a 50-J TEA CO₂ laser. In the present paper, the sparkover voltage characteristics and interferometric measurement on laser-produced plasma mainly are described, together with sparkover induction for a series of metal beads arranged equidistantly which simulate a plasma channel.     

A novel approach to deliverable power in low‐voltage DC distribution system on the basis of voltage stability

This paper proposes that a deliverable power through a low‐voltage DC distribution system has an upper limitation. The upper limitation of the deliverable power, P_lim, is explained on the basis of a voltage instability phenomenon occurring for the load with a voltage sensitivity below 1. From theoretical‐calculation results, it is pointed out that P_lim diminishes with augment in the distribution‐line length. This phenomenon becomes more distinct for the higher distribution‐line inductance per unit length. Connection of the capacitor to the receiving end of the distribution line is discussed as a method for rising P_lim. Measurements of the voltage waveform at the load terminals successfully support P_lim derived from the theoretical calculation. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.